Input arguments

Output arguments

Notes

The global integers assigned to the ISs of the local input list might not correspond to the
local numbers of the ISs on that list, but the two *orderings* are the same: the global
integers assigned to the ISs on the local list form a strictly increasing sequence.

The ISs on the input list can belong to subcommunicators of comm, and the subcommunicators
on the input IS list are assumed to be in a "deadlock-free" order.

Local lists of PetscObjects (or their subcommes) on a comm are "deadlock-free" if subcomm1
preceeds subcomm2 on any local list, then it preceeds subcomm2 on all ranks.
Equivalently, the local numbers of the subcomms on each local list are drawn from some global
numbering. This is ensured, for example, by ISPairToList().